Average rates of protein catabolism in diabetes and starvation are increased by 50-150%. Our overall objectives are to study the characteristics and possible causes of this enhanced protein degradation. We have found that several general characteristics of normal protein catabolism are strikingly altered in tissues of diabetic or starved rats. In several normal tissues there are correlations between protein subunit molecular weight and half-life, between protein isoelectric point and half-life, and between protein carbohydrate content and half-life. Each of these characteristics are reduced or absent in insulin-sensitive tissues during the accelerated protein breakdown caused by diabetes or starvation. These results suggest that degradative rates of various proteins are affected in a heterogeneous manner by diabetes or starvation. We have confirmed that catabolism is most greatly enhanced for cellular proteins of small molecular weight, basic isoelectric point and low carbohydrate content. We hope eventually to determine the biochemical explanations for the rapid protein degradation which occurs in diabetes and starvation.